Energy storage cells (also referred to herein as “cells” or “batteries”) sold for consumer use in portable electronic devices and other applications have occasional failure in the field. These cells have typically passed a wide variety of safety tests, such as those required by governmental shipping regulations and by other certification organizations, but fail after the cells have been in use over time (e.g., several months), even though there have been no other reported problems with the cells that fail. Regardless, these failures can result in the cells overheating, and in some cases, going into thermal runaway wherein the cell can ignite and burn. For example, these incidents have been reported in the media as “the burning laptop” and have resulted in the recall of millions of batteries. At least some of these failures have been attributed to a latent defect introduced during the cell manufacturing process that escapes detection during initial acceptance testing and results in an internal short circuit between the positive and negative components of a cell (electrodes or current collectors) after having been in use for some time.
Safety measures such as additives, new materials, and new designs are incorporated into the cell to address these internal short circuit failures. Some test approaches/methods have been proposed to simulate an internal short to evaluate the modified design and material features. Previous approaches/methods have included (nail or rod) penetration and crush tests. For example, the military uses a nail or bullet to penetrate the battery at a specifically designed test facility; National Aeronautics and Space Administration (NASA) uses a crush test implementing a rounded rod that is pressed into the battery at the test facility; United States Advanced Battery Consortium (USABC) test procedure includes nail or rounded rod penetration; Underwriters Laboratory (UL) uses a blunt nail crush test, and some battery manufacturers use a pinch test. Other approaches have included retrofitting a metallic particle into the “jelly roll” of a battery during manufacture, which triggers a failure upon compressing, repeated charging/discharging, sonication, thermal ramping, or overcharging/over discharging at a test facility. Still other approaches include assembling a micro-heater in the cell between the anode and separator or cathode and separator and heating the separator to its melting point at a test facility. These test methods are not representative of field failures, and cannot be readily used as a safety device for batteries.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.